Vehicle systems may include various vacuum consumption devices that are actuated using vacuum. These may include, for example, a brake booster, a fuel vapor canister etc. Vacuum used by these devices may be provided by a dedicated vacuum pump. In still other embodiments, one or more aspirators (alternatively referred to as ejectors, venturi pumps, jet pumps, and eductors) may be coupled in the engine system that may harness engine air flow and use it to generate vacuum.
Since aspirators are passive devices, they provide low-cost vacuum generation when utilized in engine systems. An amount of vacuum generated at an aspirator can be controlled by controlling the motive air flow rate through the aspirator. While aspirators may generate vacuum at a lower cost and with improved efficiency as compared to electrically-driven or engine-driven vacuum pumps, their use in engine intake systems has traditionally been constrained by both available intake manifold vacuum and maximum throttle bypass flow. Some approaches for addressing this issue involve arranging a valve in series with an aspirator, or incorporating a valve into the structure of an aspirator. Such valves may be referred to as aspirator shut-off valves (ASOVs) or aspirator control valves (ACVs). An opening amount of the valve is regulated to control the motive air flow rate through the aspirator, and thereby control an amount of vacuum generated at the aspirator. By controlling the opening amount of the valve, the amount of air flowing through the aspirator and the suction air flow rate can be varied, thereby adjusting vacuum generation as engine operating conditions, such as intake manifold pressure, change.
An example approach of controlling motive flow rate through the aspirator is shown by Emmerich et al. in U.S. Pat. No. 6,220,271. Herein, a solenoid operated ASOV controls motive flow through the aspirator based on a pressure (or a vacuum level) in a brake booster. When vacuum level in the brake booster decreases below a threshold, the ASOV is opened to enable vacuum generation at the aspirator. The vacuum generated at the aspirator is then supplied to the brake booster.
The inventors herein have identified potential issues with the above approach to motive flow control. For example, opening the ASOV for vacuum generation during certain engine conditions may adversely affect emissions. Further, by controlling the ASOV based on a pressure in the brake booster, the operation of the ASOV and the aspirator may not be sufficiently tested during vehicle emissions testing procedures. Herein, the ASOV may not be actuated open during vehicle emissions testing (e.g. the U.S. Federal Test Procedure 1975) since sufficient brake booster vacuum may be available without exercising the ASOV.
The inventors herein have identified an approach to at least partly address the above issues. In one example approach, a method for an engine is provided comprising increasing an opening of an aspirator shut-off valve (ASOV) to allow motive flow through an aspirator in response to engine speed between a first, lower speed and a second, higher speed. In this way, the ASOV may be controlled independent of brake booster conditions and other ambient conditions.
For example, an engine may include an aspirator for passive vacuum generation. In one example, the engine may be naturally aspirated wherein the aspirator may be coupled in a throttle bypass passage across from an intake throttle coupled in an intake passage. In an alternative embodiment, the engine may be a boosted engine including a compressor wherein the aspirator may be coupled across a compressor in a compressor bypass passage. In yet another embodiment, the engine may be boosted with the aspirator coupled in the throttle bypass passage across from the intake throttle. Motive flow through the aspirator may be regulated by an aspirator control valve (ACV). A controller may activate the ACV to an open position when engine speed is between a first, lower speed and a second, higher speed. In one example, the first lower speed may be a speed based on a transmission lugging limit. In another example, the second, higher speed may be based on a redline speed for the engine. The controller may adjust the ACV towards a closed position if engine speed reduces below the first lower speed or if the engine speed increases above the second, higher speed. Thus, motive flow through the aspirator may be regulated based on engine speed and not an existing vacuum level in a brake booster.
In this way, ACV operation may be controlled for vacuum generation. Controlling the motive flow rate through the aspirator based on engine speed provides a more simplified control of the ACV. Further, by modulating the ACV based on engine speed, aspirator and ACV operation may be tested reliably during emissions testing procedures. Specifically, the ACV may be exercised during an example federal emissions testing procedure. Overall, with the simplified control algorithm for the ACV, a reduction in manufacturing costs may be achieved along with enhanced emissions compliance.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.